Contact modelling of large radius air bending with geometrically exact contact algorithm

Usage of high-strength steels in conventional air bending is restricted due to limited bendability of these metals. Large-radius punches provide a typical approach for decreasing deformations during the bending process. However, as deflection progresses the loading scheme changes gradually. Therefore, modelling of the contact interaction is essential for an accurate description of the loading scheme. In the current contribution, the authors implemented a plane frictional contact element based on the penalty method. The geometrically exact contact algorithm is used for the penetration determination. The implementation is done using the OOFEM – open source finite element solver. In order to verify the simulation results, experiments have been conducted on a bending press brake for 4 mm Weldox 1300 with a punch radius of 30 mm and a die opening of 80 mm. The maximum error for the springback calculation is 0.87° for the bending angle of 144°. The contact interaction is a crucial part of large radius bending simulation and the implementation leads to a reliable solution for the springback angle

Forming limit predictions for single-point incremental sheet metal forming

peer reviewedA characteristic of incremental sheet metal forming is that much higher deformations can be achieved than conventional forming limits. In this paper it is investigated to which extent the highly non-monotonic strain paths during such a process may be responsible for this high formability. A Marciniak-Kuczynski (MK) model is used to predict the onset of necking of a sheet subjected to the strain paths obtained by finite-element simulations. The predicted forming limits are considerably higher than for monotonic loading, but still lower than the experimental ones. This discrepancy is attributed to the strain gradient over the sheet thickness, which is not taken into account in the currently used MK model

Effect of FEM choices in the modelling of incremental forming of aluminium sheets

peer reviewedThis paper investigates the process of single point incremental forming of an aluminium cone with a 50-degree wall angle. Finite element (FE) models are established to simulate the process. Different FE packages have been used. Various aspects associated with the numerical choices as well as the material and process parameters have been studied. The final geometry and the reaction forces are presented as the results of the simulations. Comparison between the simulation results and the experimental data is also made

Effect of stress relieving heat treatment on surface topography and dimensional accuracy of incrementally formed grade 1 titanium sheet parts

The forming of parts with an optimized surface roughness and high dimensional accuracy is important in many applications of incremental sheet forming (ISF). To realize this, the effect of stress relieving heat treatment of grade-1 Ti parts performed before and after forming on the surface finish and dimensional accuracy was studied. It was found that heat treatment at a temperature of 540 °C for 2 h improves the surface finish of formed parts resulting in a surface with little or no visible tool marks. Additionally, it improves the dimensional accuracy of parts after unclamping from the rig used for forming, in particular, that of parts with shallow wall angles (typically <25°). It was also noted that post-forming heat treatment improves the surface finish of parts. The surface topography of formed parts was studied using interferometry to yield areal surface roughness parameters and subsequently using secondary electron imaging. Back-scatter electron microscopy imaging results coupled with energy-dispersive X-ray (EDX) analysis showed that heat treatment prior to forming leads to tool wear as indicated by the presence of Fe in samples. Furthermore, post-forming heat treatment prevents curling up of formed parts due to compressive stresses if the formed part is trimmed

Characterization of shape and dimensional accuracy of incrementally formed titanium sheet parts with intermediate curvatures between two feature types

Single point incremental forming (SPIF) is a relatively new manufacturing process that has been recently used to form medical grade titanium sheets for implant devices. However, one limitation of the SPIF process may be characterized by dimensional inaccuracies of the final part as compared with the original designed part model. Elimination of these inaccuracies is critical to forming medical implants to meet required tolerances. Prior work on accuracy characterization has shown that feature behavior is important in predicting accuracy. In this study, a set of basic geometric shapes consisting of ruled and freeform features were formed using SPIF to characterize the dimensional inaccuracies of grade 1 titanium sheet parts. Response surface functions using multivariate adaptive regression splines (MARS) are then generated to model the deviations at individual vertices of the STL model of the part as a function of geometric shape parameters such as curvature, depth, distance to feature borders, wall angle, etc. The generated response functions are further used to predict dimensional deviations in a specific clinical implant case where the curvatures in the part lie between that of ruled features and freeform features. It is shown that a mixed-MARS response surface model using a weighted average of the ruled and freeform surface models can be used for such a case to improve the mean prediction accuracy within ±0.5 mm. The predicted deviations show a reasonable match with the actual formed shape for the implant case and are used to generate optimized tool paths for minimized shape and dimensional inaccuracy. Further, an implant part is then made using the accuracy characterization functions for improved accuracy. The results show an improvement in shape and dimensional accuracy of incrementally formed titanium medical implants

Evaluation of strain and stress states in the single point incremental forming process

Single point incremental forming (SPIF) is a promising manufacturing process suitable for small batch production. Furthermore, the material formability is enhanced in comparison with the conventional sheet metal forming processes, resulting from the small plastic zone and the incremental nature. Nevertheless, the further development of the SPIF process requires the full understanding of the material deformation mechanism, which is of great importance for the effective process optimization. In this study, a comprehensive finite element model has been developed to analyse the state of strain and stress in the vicinity of the contact area, where the plastic deformation increases by means of the forming tool action. The numerical model is firstly validated with experimental results from a simple truncated cone of AA7075-O aluminium alloy, namely, the forming force evolution, the final thickness and the plastic strain distributions. In order to evaluate accurately the through-thickness gradients, the blank is modelled with solid finite elements. The small contact area between the forming tool and the sheet produces a negative mean stress under the tool, postponing the ductile fracture occurrence. On the other hand, the residual stresses in both circumferential and meridional directions are positive in the inner skin of the cone and negative in the outer skin. They arise predominantly along the circumferential direction due to the geometrical restrictions in this direction.The authors would like to gratefully acknowledge the financial support from the Portuguese Foundation for Science and Technology (FCT) under project PTDC/EMS-TEC/1805/2012. The first author is also grateful to the FCT for the postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

Energy-efficient scheduling for a flexible flow shop using an improved genetic-simulated annealing algorithm

This is the author’s version of a work that was accepted for publication in Robotics and Computer-Integrated Manufacturing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Robotics and Computer-Integrated Manufacturing, [Volume 29, Issue 5, October 2013, Pages 418–429] DOI10.1016/j.rcim.2013.04.001[EN] The traditional production scheduling problem considers performance indicators such as processing time, cost and quality as optimization objectives in manufacturing systems; however, it does not take energy consumption and environmental impacts into account completely. Therefore, this paper proposes an energy-efficient model for flexible flow-shop scheduling (FFS). First, a mathematical model for a FFS problem, which is based on an energy-efficient mechanism, is described to solve multi-objective optimization. Since FFS is well known as the NPhard problem, an improved genetic-simulated annealing algorithm is adopted to make a significant trade-off between the makespan and the total energy consumption for implementing a feasible scheduling. Finally, a case study of production scheduling problem for metalworking workshop in a plant is simulated. The experimental results show the relationship between the makespan and the energy consumption is conflicting apparently. Moreover, an energy saving decision is performed in a feasible scheduling. Using the decision method, there can be a significant potential to minimize energy consumption while complying with the conflicting relationshipThis research was carried out as a part of the CASES project which is supported by a Marie Curie International Research Staff Exchange Scheme Fellowship within the 7th European Community Framework Program under the Grant agreement no 294931. This research was also supported by National Science Foundation of China (No. 51175262), Jiangsu Province Science Foundation for Excellent Youths (No. BK201210111), Jiangsu Province Industry-Academy-Research Grant (No. BY201220116), the NUAA Fundamental Research Fund (No. NS2013053), the Project Funded by Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the research project TIN2010-20976-C02-01 (Ministry of Science and Innovation, Spain).Dai, M.; Tang, D.; Giret Boggino, AS.; Salido Gregorio, MA.; Li, W. (2013). Energy-efficient scheduling for a flexible flow shop using an improved genetic-simulated annealing algorithm. Robotics and Computer-Integrated Manufacturing. 29(5):418-429. https://doi.org/10.1016/j.rcim.2013.04.001S41842929

Selected Contemporary Challenges of Ageing Policy

Among the scholars trying to grasp the nuances and trends of social policy, there are diverse perspectives, resulting not only from the extensive knowledge of the authors on the systematic approach to the issue of supporting older people but also from the grounds of the represented social gerontology schools. In the texts of Volume VII interesting are both distinct and coherent elements presenting the role of local, regional and global policies in the prism of the countries from which the authors originate: the Czech Republic, Slovenia, Lithuania, Latvia, Poland, Slovakia, Italy, Turkey, and the United States. The chapters show a wealth of methodological approaches to the perception of social policy and its tools. In the texts there are issues related to the idea of active ageing, discrimination against older people in the workplace, comparability of solutions friendly to employment of older adults in the Czech Republic, Poland, and Slovakia as well as focused on the importance of educational forms (universities of the third age, senior clubs, folk high schools, and other non-formal solutions) determining an active life in old age. This monograph also attempted to answer the question regarding how to transfer the idea of intergenerational learning into the realm of practice. This issue complements the chapter on the implementation of intergenerational programs in institutions providing long-term care support. The book also outlines a public policy on ageing in the perspective of the changes over the last few decades (Slovenia) and the case demonstrating solutions to accelerate self-reliance as a key to active ageing (Turkey)

Evaluating the relationship between use phase environmental impacts and manufacturing process precision

The environmental impact of most consumer products is dominated by their use phase. However, these impacts tend to be driven by the manufacture of the product’s components since components fabricated with higher precision typically allow the product to operate at higher efficiencies. This paper investigates the relationship between precision and life cycle environmental impacts by extending the traditional LCA methodology to evaluate the impact of manufacturing process precision on the functional performance of a product during its use phase. The implications of this relationship to manufacturing decision-making are also discussed as sustainability concerns may support the use of higher precision processes

Modelling and Verification of Energy Consumption in CNC Milling

Electrical energy consumption forms 99% of the environmental impact of machining operations. Whilst replacing existing machineries for more energy efficient ones does not deem possible in short term, process planning for machining with energy consumption in mind is a more accessible solution. The effect of cutting parameters on power consumption in CNC milling of 6082 T6 aluminum alloy was investigated in this paper. Mathematical models were developed to estimate the energy and power consumption in CNC milling machines. The analysis indicated that the two less studied parameters of axial and radial depth of cut have significant impact on the total energy consumption of machining processes. Increased axial and radial depth of cut not only increase material removal rate but also increase the portion of machine tool’s power consumption dedicated to material cutting. This study indicated that 82% reduction in energy consumption can be achieved through precise selection of cuttingparameters.<br/